Color image reproduction systems known in the art permit images to be captured by certain image-receptive media or devices, possibly digitized and stored, and then output onto complementary media. So, for instance, color images may be first captured on negative film and then reproduced on negative photographic paper. Such images may or may not pass through a digital intermediary. In another case, color images may be captured on positive photographic materials, known as transparencies, and then viewed directly by projection or back-illumination, or copied onto larger or smaller transparencies, or printed onto positive photographic paper. Again, such images may or may not pass through a digital intermediary. In yet another case, color images may be captured as an electronic signal by a video camera, and then viewed on a video monitor or converted to print by a device such as a thermal printer. Again, such images may or may not pass through a digital intermediary. The foregoing are just some examples of color image reproduction systems. The application of this invention is not limited to the above examples, but may be applied to other color imaging systems as well, for instance to the reproduction of reflection originals using photographic, electrostatic, or other means.
Color-imaging systems in which the image passes through a digital intermediary allow improvements to be made to an image using a single means which may be a digital computer. Thus, improvements to an image's color and tone scale as well as to its sharpness and noise can be made in a convenient and adaptable way. Furthermore, if the imaging system includes a means for rapid viewing of the changes, the content of an image can also be edited in a convenient fashion. Many of these types of improvements are known to those skilled in the art. For example, U.S. Pat. No. 4,500,919 entitled "COLOR REPRODUCTION SYSTEM" by W. F. Schreiber, discloses an image reproduction system of one type in which an electronic reader scans an original color image and converts it to an electronic image. A computer workstation and an interactive operator interface, including a video monitor, permit an operator to edit an image by means of displaying it on the monitor. When the operator has composed a desired image on the monitor, the workstation causes the output writer device to make an inked output of the reproduced image. Such systems are often referred to as "hybrid" imaging systems because they combine elements of photographic or other chemical-based imaging together with various elements of electronic imaging systems.
A hybrid color imaging system of significantly greater value would have the ability to produce appropriately rendered reproductions of input images from any of a plurality of original image-receptive media and/or devices using any of a plurality of output image-receptive media and/or devices regardless of the origin of the original input image. If this capability were incorporated in a hybrid imaging system, images originally captured on negative film, for instance, could be shown on a video monitor as well as be printed onto negative or positive photographic films or papers. Likewise, images originally captured on positive film could be shown on a video monitor as well as be printed onto negative or positive photographic films or papers. Additionally, images from various reflection media could be shown on a video monitor as well as be printed onto negative or positive photographic films or papers, or video or other forms of electronic images could be printed onto negative or positive photographic films or papers. Furthermore images from any of these input sources could be printed using a thermal, ink-jet, or electrostatic printing means as well as many other means known in the art. In all cases, it would be desirable for the final printed or displayed images to appear appropriately rendered for the reproduction medium selected to produce and/or display the final image and for the specific application of that final image.
An improved color-imaging system would also provide the capability of storing image-bearing signals or digitized images for later display in such a manner that the display device, whether it produces hard copy using photographic paper, thermal dye transfer, electrostatic, or any other printing means, or a soft copy such as a video image, is not required to make any adjustments based on the original image capture medium or image source in order to make appropriately rendered reproductions of said images.
An improved color-imaging system would further provide the capability to produce output images, from various input media or sources, that are appropriately rendered using any of a number of output or display means. In each case, images would be rendered in a way that is appropriate based on the capabilities and limitations of the specific output device and/or medium and on the specific application for which the image is being produced.
An improved color-imaging system would additionally provide the capability to mix portions of images from various input media or sources and to then produce an appropriately rendered composite image using any of the various output and display means. For instance, one might wish to merge a portion of an image captured on one medium, such as positive transparency film, with a portion of an image captured on another medium, such as color negative film, and produce a single composite image on another medium, such as a video display, so that the entire composite image has an homogeneous and appropriate appearance.
A final consideration for an improved color-imaging system is that in order to optimally display or reproduce color images, it is often necessary to correct for variations in overall exposure and color balance due to exposure control errors of image capturing devices, variations in color temperature of the taking illuminants, and other factors. These balance adjustments are particularly important for an imaging system which has the previously described capability to merge portions of several images into a composite image. Different balance adjustments, and other types of image modifications, may be necessary for each input image in order to produce a completely homogeneous-appearing composite image. A practical color-imaging system should therefore provide a convenient means to apply these balance adjustments and other image modifications. An improved hybrid color-imaging system would further provide this capability without requiring references to the origin of the input image.
Those skilled in the art will recognize the particular difficulty of successfully exchanging, storing, adjusting, and producing homogeneous-appearing composite images of merged imaging data when disparate sources of input, many of which may not be designed specifically for use in hybrid imaging systems, are to be included as potential inputs to such imaging systems.
Images on photographic films and papers, for example, are frequently used as input for hybrid imaging systems; yet these media are generally not designed specifically for purposes directly related to hybrid imaging. They are instead most often designed for direct viewing by a human observer or for printing onto other photographic materials. The different requirements for photographic negatives, photographic prints, photographic transparencies, graphic arts prints, and other forms of images result in a disparity and an inherent incompatibility among potential input image types. Image data typically derived from disparate input sources is incompatible in that it can not be directly exchanged, stored, adjusted, used to produce homogeneous-appearing composite images, or sent to an output device without requiring knowledge of the origin of each input image.
There are two fundamental causes of this incompatibility among image types. The first is that most positive imaging media are designed to be directly viewed by a human observer in a specific viewing environment. Reflection prints and most pieces of artwork, for example, are designed to be observed in a normal viewing environment, i.e., where the illumination of the image is similar in luminance level and chromaticity to the illumination of the rest of the viewing environment. Transparencies, on the other hand, are often designed to be projected in a darkened room or illuminated by back-light. These and other differences in the viewing environment will cause significant differences in a human observer's perception of an image. Imaging media designed for direct viewing by a human observer must, therefore, be designed for specific intended viewing environments. Each medium must be designed so as to properly compensate for perceptual effects that its associated viewing environment will induce in the human observer.
A measuring device, such as an input scanner in a hybrid imaging system, is of course not subject to the same perceptual effects as the human observer. As a consequence, measurements of images on disparate media will not directly correspond to the appearances of images on such media, even if those measurements correspond to CIE or other calorimetric standards and recommended practices. For example, if a typical 35 mm photographic transparency is measured calorimetrically and that colorimetry is exactly reproduced on a reflection print, the reflection print will appear to be extremely dark, much too high in luminance contrast, and cyan-blue in overall color balance. This is because the transparency material has been specifically designed to be viewed in a darkened room where perceptual effects such as general brightness adaptation, lateral brightness adaptation, and partial chromatic adaptation will be induced in the human observer such that the transparency image will appear to be properly rendered in that particular viewing environment. Because the measured colorimetric values for the transparency designed for dark projection do not correspond to the visual appearance of that transparency, colorimetric data scanned from that transparency is incompatible with data scanned from a reflection print or from any other form of image designed to be viewed in a normal viewing environment.
U.S. patent application Ser. No. 002,479 entitled DIGITAL COLOR SYSTEM AND METHOD WHICH PROVIDES VISUAL MATCH ACROSS DIFFERENT INPUT AND OUTPUT VIEWING CONDITIONS addresses one aspect of perceptual adaptation--chromatic adaptation. That application describes a color management system which transforms measured calorimetric values from images in a way that produces the corresponding calorimetric values that would be required to visually match the appearance of that image in a defined reference viewing environment.
The present invention addresses other perceptual issues, not addressed in that application, including the incompleteness of the observer's chromatic adaptation, lateral brightness adaptation (which can affect the observer's perception of luminance contrast), and general brightness adaptation (which affects the observer's perception of brightness) as they apply to input image incompatibility.
Moreover, the present invention addresses a second fundamental cause of incompatibility among input images that is also not addressed by the invention of the aforementioned application. This second fundamental incompatibility results because some input sources, such as photographic negatives and some forms of digital images, do not contain rendered output imaging information, i.e., information relating directly to an image intended to be viewed directly by an observer. These input sources produce rendered output images, intended for viewing, only when printed or otherwise output to an appropriate device and/or medium. Colorimetric data measured directly from such input sources is therefore fundamentally incompatible with colorimetric data measured directly from reflection prints, slides, and other forms of rendered images. Colorimetric data measured directly from a photographic negative, for example, would essentially correspond to the appearance of the negative itself rather than to a rendered positive image that would result if, for example, the negative were to be optically printed on to a photographic paper using and enlarger or other printing means.
As a result of these two fundamental causes of input image incompatibility, imaging data derived from photographic negatives, photographic transparencies, photographic and other forms of reflection images, and electronic sources of input cannot be used together to meet the interchange, storage, adjustment, and image-merging objectives described for this invention unless such data are given special treatment.
U.S. patent application Ser. No. 931,889 entitled Methods And Associated Apparatus for forming Image Data Metrics which Achieve media Compatibility for Subsequent Imaging Applications, filed in the names of E. Giorgianni and T. Madden, provides one method for meeting these stated objectives. In that application, a system is described in which compatibility of the input images is achieved by removing, as far as possible, all media-specific properties of each input medium. Compatibility is achieved by the transformation of each input to a common meaning or interpretation, i.e., the colorimetry of the original scene, or other source of exposure, which caused the input image to form on the input imaging device and/or medium.
While that solution is optimal for certain types of imaging systems, other types of systems may have different objectives which cannot be achieved by that approach. In graphic arts and desktop imaging, for example, the input image to be scanned, not the original scene, is generally considered to be the original image, and the imaging system must be capable of making a copy or other type of reproduction that is a visual match of the input image. In addition, these types of imaging systems may also require the capability for the straightforward generation of colors to user-provided calorimetric specifications.
It is the intent of the present invention, therefore, to provide novel methods and means which produce compatibility among inherently disparate forms of image inputs and which achieve that compatibility for image storage, adjustment, manipulation and merging in a way that additionally provides the capability to produce copies and other forms of appearance matches on any of a plurality of output devices and media and under any of a plurality of output viewing conditions. It is a further intent of this application to include the capability for producing calorimetrically specified colors on any output device and/or medium.